Characterization of Feruloyl Esterases Produced by the Four Lactobacillus Species: L. amylovorus, L. acidophilus, L. farciminis and L. fermentum, Isolated from Ensiled Corn Stover.

Zhenshang Xu,Jian Kong,Huiying He,Tingting Guo,Susu Zhang

doi:10.3389/fmicb.2017.00941

Abstract

Lactic acid bacteria (LAB) play important roles in silage fermentation, which depends on the production of sufficient organic acids to inhibit the growth of undesirable microorganisms. However, LAB are not able to degrade cellulose and hemicellulose. Bacteria and fibrolytic enzymes are usually used as inoculants to improve the silage quality and digestibility. In the present study, we isolated four Lactobacillus strains (L. amylovorus CGMCC 11056, L. acidophilus CCTCC AB2010208, L. farciminis CCTCC AB2016237 and L. fermentum CCTCC AB2010204) with feruloyl esterase (FAE) activities from ensiled corn stover (CS) by a plate screening assay. The genes encoding FAEs were cloned and hetero-expressed in Escherichia coli. The optimal temperature and pH of these purified enzymes ranged from 45 to 50°C and from 7.0 to 8.0, respectively. They could hydrolyze hydroxycinnamoyl esters in a substrate-specific manner when methyl ferulate, methyl caffeate, methyl ρ-coumarate and methyl sinapinate were used as substrates. Moreover, these four FAEs were able to hydrolyze CS to release hydroxycinnamic acids. Furthermore, these strains could degrade hydroxycinnamic esters, and L. amylovorus CGMCC 11056 was the most efficient strain among these four isolates. These results provided a new target for the development of inoculants to improve silage quality and digestibility.

Highlights

Lactic acid bacteria (LAB) are widely distributed in the surface of plants and fermented dairy foods, where they produce organic acids, enzymes and metabolites, contributing to the organoleptic property, flavor and long-shelf life of final products (Torino et al, 2015; Zannini et al, 2016)
To identify these isolates at species level, their 16S rRNA genes were sequenced and aligned, which showed 100, 99, 99, and 100% identity with L. amylovorus 14LAB1, L. acidophilus NCFM, L. farciminis KCTC3681 and L. fermentum IFO3956, respectively. Based on these phenotypic characteristics, combined with the 16S rDNA sequences, these four isolates were identified as L. amylovorus, L. acidophilus, L. farciminis and L. fermentum
The results showed that these four Lactobacillus strains could efficiently hydrolyze the model substrates except L. farciminis Center for Type Culture Collection (CCTCC) AB2016237 and L. fermentum CCTCC AB2010204 which showed low hydrolytic activities to methyl sinapinate (Table 5)

Summary

Introduction

Lactic acid bacteria (LAB) are widely distributed in the surface of plants and fermented dairy foods, where they produce organic acids, enzymes and metabolites, contributing to the organoleptic property, flavor and long-shelf life of final products (Torino et al, 2015; Zannini et al, 2016). These bacteria have beneficial effects on intestinal tracts in human and animals (Yu et al, 2016; Zhang et al, 2016). Feruloyl esterase (FAE), considered as an important accessory enzyme which is able to cleave the ester linkage between the ferulate and polysaccharide chain in the cell walls, is attracting more and more attention (Crepin et al, 2004; Koseki et al, 2009)

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